TIME
OF
COMPLETION_______________
NAME__SOLUTION___________________________
DEPARTMENT OF NATURAL SCIENCES
PHYS 1112, Exam 2
Version 2
Total Weight: 100 points
Section 1
October 25, 2013
1.
Check your examination for completeness prior to starting. There are a total of nine (9)
problems on six (6) pages.
2.
Authorized references include your calculator with calculator handbook, and the
Reference Data Pamphlet (provided by your instructor).
3.
You will have 50 minutes to complete the examination.
4.
The total weight of the examination is 100 points.
5.
There are six (6) multiple choice and three (3) calculation problems. Work five (5)
multiple choice and three (3) calculation problems. Show all work; partial credit will be given for
correct work shown.
6.
If you have any questions during the examination, see your instructor who will
be located in the classroom.
7.
Start:
Stop:
9:00 a.m.
9:50 a.m.
PROBLEM
POINTS
1-6
25
7
25
8
25
9
25
TOTAL
100
PERCENTAGE
CREDIT
CIRCLE THE SINGLE BEST ANSWER FOR ALL MULTIPLE CHOICE QUESTIONS
UNLESS INSTRUCTED OTHERWISE. IN MULTIPLE CHOICE QUESTIONS WHICH
REQUIRE A CALCULATION SHOW WORK FOR PARTIAL CREDIT.
1. Consider three resistors with unequal resistances connected in series to a battery. Which
of the following statements are true? Check all that apply.
a. The voltage across each of the resistors is the same and is equal in magnitude to the voltage
of the battery.
b. The algebraic sum of the currents flowing through each of the three resistors is equal to
the current supplied by the battery.
(5)
c. The equivalent resistance of the combination of resistors is greater than the resistance of
any one of the three resistors.
d. The current flowing through each of the resistors is the same and is equal to the current
supplied by the battery.
e. The algebraic sum of the voltages across the three resistors is equal to the voltage supplied
by the battery.
2. A proton moves in the plane of this paper toward the top of the page. A magnetic field is
also in the plane of the page and directed toward the right. The direction of the magnetic
force on the proton is described by which of the following?
a. Toward the right edge of the page.
b.
Downward into the page.
c.
Toward the top of the page.
d.
Upward out of the page.
e.
Toward the left edge of the page.
(5)
3.
What happens to the magnitude of the magnetic field inside a long solenoid if the current
is reduced to one-half of its original value?
a.
It becomes four times larger.
b.
It becomes twice as large.
c.
It is unchanged.
d.
It becomes one-half as large.
(5)
4. Which of the following statements are true? Check all that apply.
a. Scientists have evidence that single isolated magnetic poles, called magnetic
monopoles, exist.
b. Earth's geographic north pole is actually a magnetic south pole.
(5)
c. Earth's geographic south pole is also a magnetic south pole.
d. The north pole of a bar magnet will attract the south pole of another bar magnet.
a. The north poles of two bar magnets will attract each other.
5. A current carrying loop of wire lies flat on a table top. When viewed from above, the
current moves around the loop in a counterclockwise sense. For points INSIDE the loop,
the magnetic field caused by this current
a.
Circles the loop in a counterclockwise direction.
b.
Points straight down.
c.
Points straight up.
d.
Circles the loop in a clockwise direction.
e.
Is zero.
6. A horizontal wire carries a current straight toward you. From your point of view, the
magnetic field at a point directly below the wire points
a.
To the right.
b.
To the left.
c.
Directly toward you.
d.
Directly away from you.
e.
Vertically upward.
(5)
PHYS 1112 Exam 2, Version 2
Fall 2013
3
7. An electron at point A in the figure below has a speed of 1.30×106 m/s. (Hint: me = 9.11 x
10-31 kg.)
a. Find the magnitude of the magnetic field that will cause the electron to follow the
semicircular path from A to B.
r
mV
|q|B
B
mV (9.11  10 31 kg)(1.30  10 6 m / s)

 1.48  10  4 T
19
|q|r
(1.60  10 C )(0.0500 m)
b. Find the direction of the magnetic field that will cause the electron to follow the
semicircular path from A to B.
Into the page.
8. A straight 3.00 m wire carries a typical household current of 1.50 A (in one direction) at a
location where the earth's magnetic field is 0.550 gauss from South to North.
PHYS 1112 Exam 2, Version 2
Fall 2013
4
a. Find the direction of the force that our planet's magnetic field exerts on this cord
if is oriented so that the current in it is running from west to east.
Out of the page (upward).
b. Find the magnitude of the force that our planet's magnetic field exerts on this cord
if is oriented so that the current in it is running from west to east.
F  IBl sin   (1.50 A)(0.550  10 4 T )(3.00 m) sin(90.0 o )  2.475  10 4 N
c.
Find the direction of the force that our planet's magnetic field exerts on this cord
if is oriented so that the current in it is running vertically upward.
West (to the left)
d. Find the magnitude of the force that our planet's magnetic field exerts on this cord
if is oriented so that the current in it is running vertically upward.
The same as in (b)
e. Is the magnetic force ever large enough to cause significant effects under normal
household conditions?
No.
9. Given the network, write equations that would allow you to solve for the currents in each
resistor. Label and indicate your choices for current directions. DO NOT SOLVE THE
EQUATIONS. You MAY nevertheless solve the equations for the extra 5 points, if
correct.
PHYS 1112 Exam 2, Version 2
Fall 2013
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Different sets of equations are possible depending on the choice of currents and loops. One
example is below: (I1 is in the leftmost branch, downward. I2 is in the central branch, downward,
I3 is in the rightmost branch, downward.) Left loop – counterclockwise direction, right loop –
counterclockwise direction. Note that I dropped the units.
I1  I 2  I 3  0
20  2I 1  14  4I 2  0
36  5I 3  4I 2  0
PHYS 1112 Exam 2, Version 2
Fall 2013
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